Numerous applications exist for a beam transmissometer that is low in cost, relatively stable, and consumes very little power. In this paper we present the design and calibration of a beam transmissometer that is constructed with P.V.C. to simplify the design and minimize costs, contains stable temperature compensated electronics, and consumes less than 150 milliwatts of power. Accuracy and stability with proper calibration and careful use will provide data with an error of less than 0.5% transmission.